Diesel engines are widely used in heavy duty trucks and off road vehicles due to their fuel efficiency and high power outputs. Environmental regulatory agencies have pushed ever stringent regulations on all internal combustion engines, including Diesel engines on gaseous as well as particulates (soot) emissions. In order to meet today's and tomorrow's stringent emission requirements, modern diesel engines are equipped with diesel particulate filters (DPF's), as well as onboard technologies to evaluate the status of DPF. In course of time, particulate matter (soot) will be deposited inside the DPFs which tend to clog the filter and hence generate a back pressure in the exhaust system, negatively impacting the fuel efficiency. To remove the soot build-up, regeneration (active or passive) of the DPF must be done as an engine exhaust after treatment process at pre-determined time intervals. Since the regeneration process consume fuel, a robust and efficient operation based on accurate knowledge of the particulate matter deposit (or soot load) becomes essential in order to keep the fuel consumption at a minimum.
Diesel engines have come a long way in the area of emission control technologies in the last couple of decades. One of the areas in which engine technology made great strides is in the reduction of particulate matter (PM) emissions via diesel particulate filter (DPF). However, as the PM or soot is retained by the filter, the filter passageway increasingly becomes more restrictive resulting in elevated back pressure in the exhaust. This furthers results in lower fuel efficiency for the engines since the pistons have to exert more pressure to purge the exhaust gas.
One effective way to address this problem is to burn the soot load in the DPF periodically either by injecting more fuel in the engine or by a separate combustor upstream of the DPF with the aid of a diesel oxidation catalyst (DOC). The latter is known as active regeneration of DPF and is commonly used for DPF. Here a fuel doser is used to raise the exhaust gas temperature to burn off the soot load in DPF. The timing and amount of fuel dosing is critical in ensuring optimal performance of DPF functions.
The performance efficiency of a DPF with active regeneration is dependent on the accuracy of soot load estimation. Current soot load estimation is based on differential pressure measurement across the DPF whose accuracy can vary up to 50% from the true soot load. As a result, fuel dosing for active regeneration may not be optimal. This can result in significant loss in fuel efficiency if the estimate is higher than real value (since more fuel need be used), or in serious DPF damage if the estimate is less than the real value when the filter may be nearly clogged. In the latter scenario, there is also a fuel penalty due to increased back pressure in the exhaust. Also, fuel dosing for active regeneration may not be optimal. It has been shown that fuel penalty caused by regeneration (2.2% to 5.3%) can be more than fuel penalty due to backpressure (1.8% to 2.2%).
Diesel particulate filters were first used in the 1980's to remove the particulate matter/soot from the exhaust of the Diesel engine with an efficiency level of 90% or more. These filters are mostly made of ceramic materials and can withstand high temperatures. The deposited soot in the filter cavities may result in higher back pressure causing overall efficiency of the diesel engine to drop by as much as 2%. Also, a clogged filter may fail prematurely. As a result, the deposited soot in the DPF is periodically cleaned, generally by means of a process of regeneration or burning out the soot. In active regeneration, fuel is injected in a chamber right before the DPF, thus raising the exhaust temperature high enough to burn the soot inside DPF cavities. Other methods, such as microwave heating, have been proposed to clean the DPF. Fuel dosing remains the most prevalent method of active regeneration. The timing and amount of fuel dosing is critical in ensuring optimal performance of DPF functions. As a result, fuel dosing for active regeneration may not be optimal.
What is needed are improved methods for detecting the flow capability of a diesel particulate filter. An instantaneous soot load sensor based on electrical capacitance sensor is shown and described herein, and also regeneration systems utilizing such a sensor, in various embodiments of the present invention as an alternative for soot load estimation.